Ion lens system



c. E. BURDG 3,096,436

July 2, 1963 ION LENS SYSTEM 2 Sheets-Sheet 1 Filed Dec. 9, 1960 FIGJ NVENTOR CHARLES E BURDG WWQM ATTORNEY C. E. BURDG ION LENS SYSTEM July 2, 1963 2 Sheets-Sheet 2 Filed D80- 9, 1960 INVENTOR CHARLES E- BURDG j /AM 5 m ATTORNEY United States Patent 3,096,436 IQN LENS SYSTEM Charles E. Bnrdg, Sutiield, Conn, assignor to Combustron Engineering, Inc, Windsor, Conn, a corporation of Delaware Filed Dec. 9, 1960, Ser. No. 74,853 6 Claims. (Cl. 25tl-4l.9)

This invention relates to an improved ion focusing mechanism comprising a removable ion lens system tor a mass spectrometer and particularly to a lens system which may be aligned and assembled on the bench and inserted into and removed from the mass spectrometer as a unit.

An object of this invention is a self-contained ion lens system unit.

A further object is an ion lens unit having means for feeding a potential to the lens and a shield protecting the ion beam from stray fields from the feeding means.

A further object is a lens unit removable and replaceable as a unit and including a stray field shield.

Other objects and advantages will be apparent from the following specification and the accompanying drawings in which:

FIG. 1 is a side view of a mass spectrometer.

FIG. 2 is a sectional view of the ion lens system unit in position in the spectrometer.

FIG. 3 is a perspective view of the lens unit partially removed from its support.

In the use and maintenance of mass spectrometers incorporating a lens system, it is desirable that the lens be readily removable for cleaning and adjusting, and readily replaceable into a selected aligned position in the spectrometer to properly focus and accelerate the ion beam.

By the present invention I have provided a lens system including two focusing and accelerating plates and two collimating plates in a single unit which may be readily removed and replaced. The unit includes locating and positioning means cooperating with locating and positioning means on the spectrometer for accurately positioning the lens system. The lens also includes means for conducting accelerating voltages to the accelerating plates, and a shield for protecting the ion beam from fields that may be created by the conducting means. I have thus provided a compact unitary lens system which may be readily removed from the spectrometer tube after the vacuum has been broken and may be readily replaced or another lens system substituted.

The lens system chosen to illustrate my invention is shown incorporated in a mass spectrometer of the type shown in application Serial No. 45,891, filed July 28, 1960, by Charles E. Burdg for Vacuum Lock, and in an application filed on even date herewith by Charles E. Burdg for Ion Generating and Focusing Mechanism to which reference may be made for further details of the mass spectrometer. In general, the spectrometer consists of an ion source .10 supported for movement transversely of the ion stream from said source in a rotatable plate 12 rotatably mounted in air tight relation on a stationary plate 14. The ion source will create a stream of ions which are pnoiected along the interior of the tube '16 and deflected by the magnet 18 to direct selected sets of ions to the detector 20 which is connected with the counter 22 to count the number of ions in the stream of ions that reach the detector. The ions are produced on a ribbon 24 that is heated fnom an electrical source 25 to drive electrons out of the coating on the ribbon 24 and thus produce positive ions of the coating material. The ribbon 24 is encased in a block 26 having a slit 28 therein through which the ion stream is projected. The block 26 and the ribbon 24 are pnovided with a high positive voltage from a DC. source 36. The lens system being at a lower DC. voltage and the spectrometer being at 0 or ground voltage 3,096,436 Patented July 2, 1963 provide an accelerating force for the ions expelled or projected from the ribbon 24.

The stationary member 14 is provided with an aperture 32 aligned with the tube 16. A ring 34 has a passageway 36 extending therethrough and forms a body or main support of the lens system. A ring 38 secured to or integral with the ring 34 has an outer surface 40 (FIG. 3) contoured to fit the inner surface 42 of the passageway 32, and align the lens system with the tube 16. A locating dowel '43 carried by the ring 38 cooperates with the slot 44 in a ring 46 secured to the inner surface 42 of the passageway 32 and serves to position or orient the lens system around the axis of the tube 16. The surface 48 of the ring 46 cooperates with the surface 50 of the ring 38 to position the lens system longitudinally of the tube 16. The lens system is thus spaced from and oriented with respect to the slit 28 and the ribbon 24 (FIG. 2).

The body 34 of the lens system is flatted at opposite sides 52 to receive insulating plates 54 extending axially outward from the ring or body member 34. A first accelerating plate '61 is secured as by screws 56 to the outer ends of the insulating plate 54. The accelerating plate 61 is shown as comprising a pair of plates 58 spaced to provide a slit 60 between the plates. A second accelerating plate 63- comprising the spaced plates 62 similar to the spaced plates 58 is secured to insulating plates 54 by screws and is spaced slightly down-stream from the first accelerating plate. A positive voltage which is about 80% of the voltage of the ribbon 24 is applied via the wires 64 and screws 56 to the plates 58 to provide an accelerating and focusing voltage of about 20% of the voltage applied to the ribbon. A second voltage of about 10% of the ribbon voltage is applied to the focusing plates 62 via the wires 66 and screws 65 to provide an accelerating and focusing voltage of about 90% of the ribbon voltage between the second accelerating plate and the ribbon. These wires 64 and 66 are led through suitable insulated holes in the ring 34 to a terminal plate 68 in the tube 16, and are thus led from the inside to the outside of the spectrometer tube 16 to provide an electrical connection from the DC. source outside of the spectrometer into the highly evacuated chamber 70 inside of the tube 16. It should be understood that a suitable push-in plug connection could be substituted forthe connection shown, which is made by securing the wires under the nuts on the inside of the terminal board, if desired, so that the electrical connection could be made incident to the act of inserting the lens system into the recess 32.

Collimating plates are arranged at opposite sides of the body or ring 34 and are arranged downstream of the accelerating plates. The first collimating slit is formed between adjustable plates 72 secured to the upstream face of the ring 34 and the second collimating slit 74 is formed between adjustable plates 76 (FIG. 2) secured to the downstream face of the body or ring 34. These plates are arranged at ground or zero potential and provide an additional accelerating force to the positively charged ions. The accelerating plates 58 and 62 are spaced some what further apart transversely, to provide a wider slit, say about of an inch, than the slit provided by the collimating plates, which may be about 20 thousandths for the first collimating plates and 10 thousandths for the second collimating plates. The accelerating plates are placed closer together axially than the collim-ating plates .(FIG. 2).

Secured to the downstream face of ring 34 is a flange 78 carrying a tail pipe or shield 39 forming an extensionof the passageway 36 through the ring 34. The wires 64, 66, pass across a flatted portion 82 of the flange 78 and outside of the pipe 36. The pipe 80 and the ring '34 act as shields to prevent stray electrical or magnetic fields produced by wires 64, 66, from influencing the ion beam passing through the passageway 36 in the ring 34 or the passage way 84 in the pipe 80 on its way to the detector 20.

A removable access plate '86 is provided on the tube 16 to provide access to the interior of the terminal board 68 to disconnect the wires 64 and 66 when it is desired to remove the lens system unit.

From the above description it will be apparent that I have provided a removable lens system, including two accelerating plates, two collimating plates, a stray field shield, and positioning and locating means which may be removed from and inserted into a support in the stationary plate 14 as a unit.

It is to be understood that the invention is not limited to specific environment herein illustrated and described, but may be used in other ways without departure from its spirit, and that various changes can be made which would come within the scope of the invention which is limited only by the appended claims.

In operation the entire lens system including the accelerating plates, the collimating plates and the shield may be assembled and aligned on the bench and then inserted into the supporting socket in the stationary member 14 as a unit. The socket 42, cooperating with the exterior of the ring 38, will act to align the unit axially with the tube 16 and the dowel 43 and its cooperating slot 44 will act to align the system circumferentially. Gravity will hold the unit down onto the ring 46 so that the shoulder St) on the ring 40 will locate the unit axially of the tube 16 and position the unit with respect to the ion source 24, 28. The wires 64., 65 may then be connected to the connections on the terminal board 38 and the access plate 86 replaced. The tube 16 may then be evacuated to provide a vacuum chamber closed at one end by plates 12 and 14 and ion source and the machine placed in operation.

The reverse procedure is followed in removing the unit. The vacuum in tube 16 is destroyed and the access plate removed. The wires 64, 66 are then disconnected. With the hole or socket in the plate 12 aligned with the socket 42 and the ion generating unit 10 removed from its socket closing position in said hole or socket in which it is supported in plate 12, the entire lens system is removed by pulling it out through the socket 42 and the aligned hole in the rotary plate 12. The unit may then be serviced or replaced by another unit.

I claim:

1. In a mass spectrometer an ion source providing a stream of ions and supported on said spectrometer in a plate movable transversely of said stream, an ion lens system unit supported independent of said source and comprising a body having a passageway extending therethrough and contoured to telescopically fit a fixed support in said mass spectrometer, locating means in said fixed support cooperating with said body for positioning said body axially and circumferentially of said ion stream and in said fixed support adjacent said source and in the path of said ion stream with said stream passing through said passageway, insulating means carried by said body and extending axially thereof, a first pair of focusing and accelerating plates supported by said insulating means and extending transversely of said body and forming a transversely extending slit aligned with said passageway, means for applying an ion focusing andaccelerating voltage to said plates comprising wires extending longitudinally of said body, downstream of said ion stream from said plates, a tail pipe carried by said body forming a passageway for said stream downstream of said body and means directing said wires outside of said tail pipe to a voltage source outside of said spectrometer.

2. In a mass spectrometer, an ion source providing a stream of ions and supported on said spectrometer in a plate movable transversely of said stream, a unitary ion lens supported in close proximity to said source in a structure comprising a plate fixed on said spectrometer having an upwardly extending aperture and forming a sliding support for, and an air tight seal with, said movable plate, said lens having a telescopic sliding fit with said upwardly extending aperture in said fixed plate and insertable as a unit in a downward direct-ion into, and removable as a unit in an upward direction from, said fixed plate, said lens including a body having locating and positioning means cooperating with said structure and rendered effective by sliding said body into said aperture for locating and positioning said lens in said structure, said lens being held in position by gravity, a pair of spaced, aligned, slitted accelerating plates supported on and insulated from said body for accelerating and focusing an ion stream, and means for applying an accelerating voltage to said accelerating plates.

3. In a mass spectrometer having a vacuum chamber, an ion source producing a stream of ions in said chamber and supported on said spectrometer in a plate forming one side of said chamber and movable transversely of said stream, a stationary plate fixed on said spectrometer and forming a sliding support for, and an air tight seal with, said movable plate, a unitary ion lens for use in said chamber, said stationary plate supporting and locating said lens in said ion stream in the spectrometer chamber adjacent to and independent of said source, said lens comprising a body having a passageway therethrough for said stream, insulating means supporting focusing and accelerating plates on said body, collimating plates supported on said body downstream of said accelerating plates, a tail pipe aligned with said passageway downstream of said body, wires for conducting accelerating voltage connected to said accelerating and focusing plates, and extending downstream of said accelerating plates through said body inside said chamber and outside of said tail pipe to isolate stray fields from said stream, and detachable means connecting said wires to a voltage source outside of said chamber.

4. Ina mass spectrometer, an elongated vacuum chamber for receiving a stream of ions, means for supporting an ion source adjacent the entrance of said chamber, a unitary ion lens system including accelerating and collimating plates, means for suppoiting said lens system in said stream adjacent said source in fixed relation to said chamber and independent of said source, said lens system supporting means comprising an upwardly extending aperture in said chamber for slidably receiving said lens system, means in said aperture cooperating with locating means on said lens system locating and positioning said lens incident to sliding of said lens into said aperture, said lens system being urged into position by gravity and retained in position solely by gravity and the fit of said system in said aperture.

5. In a mass spectrometer, a tube for receiving a stream of ions, means for supporting an ion source adjacent the entrance to said tube, a unitary ion lens system including accelerating plates, means, including a socket, slidably receiving and locating said lens system in said stream, adjacent the entrance to, and in fixed relation to, said tube, and adjacent to, and independent of, said source, said lens system also including a body having a passageway therethrough for said stream and a tail pipe carried by, and extending downstream from, said body, aligned with said stream and the walls of said chamber, surrounding said stream and spaced from said walls, conductors for applying an accelerating voltage to said plates located downstream of said plates, in the space between said pipe and said walls and shielded from said stream by said pipe, said lens system including said body, said plates and said tail pipe insertable in, and removable from, said socket as a unit independent of said source.

6. In a mass spectrometer, an ion stream source, a lens system including accelerating plates, receiving and directing said stream, socket means having walls telescopically receiving and positioning said lens and supporting said source, a tubular chamber extending downstream from said socket means; said source and said walls closing, and forming one end of, said chamber, an open ended fmoular shield having imperforate walls surrounding said stream and extending downstream from said lens inside of, and spaced from the Walls of, said chamber, conducting means for accelerating voltage for said plates located between said shield and said chamber walls downstream of said lens.

References Cited in the file of this patent UNITED STATES PATENTS Rickard et a1 Nov. 3, 1959 

6. IN A MASS SPECTROMETER, AN ION STREAM SOURCE, A LENS SYSTEM INCLUDING ACCELERATING PLATES, RECEIVING AND DIRECTING SAID STREAM, SOCKET MEANS HAVING WALLS TELESCOPICALLY RECEIVING AND POITIONING SAID LENS AND SUPPORTING SAID SOURCE, A TUBULAR CHAMBER EXTENDING DOWNSTREAM FROM SAID SOCKET MEANS; SAID SOURCE AND SAID WALLS CLOSING AND FORMING ONE END OF, SAID CHAMBER, AN OPEN ENDED TUBULAR SHIELD HAVING IMPERFORATE WALLS SURROUNDING SAID STREAM AND EXTENDING DOWNSTREAM FROM SAID LENS INSIDE OF, AND SPACED FROM THE WALLS OF, SAID CHAMBER, CONDUCTING MEANS FOR ACCELERATING VOLTAGE FOR SAID PLANTS LOCATED BETWEEN SAID SHIELD AND SAID CHAMBER WALLS DOWNSTREAM OF SAID LENS. 